1. Field of the Invention
The present invention is generally related to the refining and processing of high density or heavy crude oil. More specifically, the invention pertains to an improved process for upgrading a heavy crude oil feedstock into an oil that is less dense or lighter that the original heavy crude oil feedstock.
2. Background
A variety of enhanced oil recovery (EOR) techniques permit the recovery of heavy oils from otherwise unproductive wells, including steam flooding, carbon dioxide flooding, and fire flooding. During EOR, a surfactant is typically used which causes the formation of underground oil/water emulsions. After being pumped to the surface, the oil and water portions of the emulsions are separated, after which the oil is passed on for further processing and the water is reused in the oil recovery operation.
Processes used in the upgrading of heavy oils to give lighter and more useful oils and hydrocarbons are generally of the carbon rejection or hydrogen addition type. Both procedures employ high temperatures (usually greater than 400.degree. C.) to "crack" the long chains or branches of the hydrocarbons that make up the heavy oil. In the carbon rejection process, the heavy oil is converted to lighter oils and coke. The formation of coke is prevented, however, in the hydrogen addition process by the addition of high pressure hydrogen. In some carbon rejection processes, the coke is used elsewhere in the refinery to provide heat or fuel for other processes. Both processes result in an upgrading of the heavy oil feedstock to less dense or lighter oils and hydrocarbons.
A process for the thermal and catalytic rearrangement of heavy oils and other similar feedstocks is described by de Bruijn et al. in U.S. Pat. Nos. 5,104,516 and 5,322,617, the contents of which are hereby incorporated by reference. In the disclosed processes, a heavy oil/water or feedstock/water emulsion is reacted with synthesis gas in the presence of a catalyst to reduce the viscosity and density of heavy oil thus making it more amenable for transportation by a pipeline. The disclosed process provides for the recovery of hydrogen and carbon dioxide gases as by-products and the recycling of carbon monoxide back into the rearrangement process. Use of a bifunctional catalyst present in about 0.03 to about 15% under conditions and pressures that facilitate both the water gas shift reaction and the rearrangement of hydrocarbons is described. The bifunctional catalyst includes an inorganic base and a catalyst containing a transition metal such as iron, chromium, molybdenum or cobalt.
The water gas shift reaction is an industrial process in which carbon monoxide (CO) and water (H.sub.2 O), in the form of steam, are reacted in the presence of a catalyst to give carbon dioxide (CO.sub.2) and hydrogen (H.sub.2) as shown in the following equation: EQU CO(g)+H.sub.2 O(g)CO.sub.2 (g)+H.sub.2 (g)
In the process disclosed by de Bruijn et al. the water gas shift reaction is used to generate the hydrogen used to rearrangement of the hydrocarbons within the feedstock, and also to produce excess gas which is recovered as by-products. As disclosed, the source of CO may be carbon monoxide mixed with water, synthesis gas or generated in-situ from the decomposition of methanol.
Synthesis gas (syngas) is a mixture of hydrogen (H.sub.2) and carbon monoxide (CO) typically in a range of ratios between about 0.9 to about 3.0. It is commonly made by the controlled combustion of methane, coal, or napthas with oxygen to give a mixture of gases including hydrogen (H.sub.2), carbon monoxide (CO), carbon dioxide (CO.sub.2), hydrogen sulfide (H.sub.2 S), carbonyl sulfide (COS), and others. It is conventional to "clean-up" the produced combustion gases to give pure synthesis gas. A critical prerequisite for the use of syngas in reactions catalyzed by transition metals is the removal of sulfur containing compounds, such as H.sub.2 S or COS, formed from sulfur compounds in natural hydrocarbons or coal. In addition, soot generated during the combustion process is removed using water-based washing or scrubbing techniques thus cooling the syngas significantly.
The process disclosed by de Bruijn et al., also known as CANMET technology, suffers from significant deficiencies when practiced on an industrial scale. Specifically, the CANMET technology:
(1) Lacks a suitable source for synthesis gas within the process scheme;
(2) Generates waste products such as coke, heavy oil residues, and spent catalyst that must be disposed of in an environmentally conscious manner;
(3) Generates water highly contaminated with hydrocarbons that require significant treatment before being released to the environment;
(4) Requires an economic source of heat for the upgrading/rearrangement reactions;
(5) Prefers a separate sulfiding step to activate the catalysts utilized in the upgrading/rearrangement reactions;
(6) Is limited by the slow kinetics of the water gas shift reaction; and,
(7) Has problems with the stability and breakdown of the heavy oil/water emulsion feedstock.